Some commercially available liquid stirring apparatuses contain stirring heads fixed to the container lids by means of drive shafts or the like whilst others have stirring heads fixed to the container bottoms by drive shafts or the like.
A stirring apparatus with a stirring head fixed to the container lid by a drive shaft usually requires that the driving means is disposed on the container lid. This type of structure has at least three disadvantages: first, the container lid is heavy and is not easy to open or close; secondly, a user touching the vessel lid may get an electric shock if the liquid in the container has overflowed or splashed onto the container lid by boiling or high speed rotation of the stirring head; thirdly, it is not easy to wash the stirring head because it is fixed on stirring hear drive shaft of the container lid, and a gap between the stirring head and the drive shaft is difficult to clean.
In the other kind of liquid stirring apparatus having a stirring head fixed to the container bottom by the stirrer head drive shaft, the shaft or mechanism connecting the shaft to the driving means extends through the container bottom into the interior of the container. This type of structure has at least three disadvantages: first, the process for manufacturing the shaft or shaft connecting mechanism of the driving means is complicated, especially the necessary sealing arrangement for the drive shaft in the container bottom which can be very complicated, and the requirement that the material of the seal must be capable of withstanding high temperatures considering the liquid in the container may be heated to boiling point; secondly, it is not easy to wash the part of the container bottom where the stirrer hear drive shaft or connecting rod passes through; thirdly, it is not easy to wash the stirring head as it is fixed on the bottom connecting rod or shaft, and the gap between the stirring head and the connecting rod or shaft is difficult to clean.
WO2006/050900 entitled “Appliance and method for preparing a froth from a food liquid” discloses that the rotatable stirrer is positioned in a tank, i.e. container, by a positioning means. The positioning means is a protrusion or a depression comprising an integrally formed moulded wall at the bottom of the tank. This disclosure also describes a magnetic drive mechanism which does not require a mechanical connection to the stirrer to drive it. With a positioning means comprising a protrusion or a depression in the bottom wall of the container, there are at least three disadvantages with this kind of structure: first, as the protrusion or depression is for locating the stirrer, the shape thereof is very precise, which cannot be easily produced by punching a recess or bulge in the vessel wall, the manufacture process is therefore made more complicated; secondly, it is difficult to wash the protrusion or the depression; thirdly, the stirring head may slip off of the protrusion or depression when it is rotating at high speed.